Pulse width modulation (PWM) may be used to control a switching-based voltage regulator (VR) to transfer charge from a source to a voltage rail.
A conventional PWM controller may include a counter and a delay-locked loop (DLL), referred to herein as a hybrid PWM controller. A conventional hybrid PWM controller may count pulses of a system clock based on a duty cycle command, and generate an initial pulse synchronous with the system clock. A conventional hybrid PWM controller may provide the initial pulse to the DLL to generate multiple phase-shifted versions of the initial pulse. A conventional hybrid PWM controller may select a one of the phase-shifted versions of the pulse to set a set/reset (RS) flip-flop during a leading edge modulation (LEM) cycle, and may select another one of the phase shifted versions of the initial pulse to reset the RS flip-flop during a trailing edge modulation (TEM) cycle. The RS flip-flop outputs a resultant phase-shifted pulse as a PWM signal to control a switching-based VR.
Conventionally, a dedicated DLL is used for each PWM signal of multiple VRs, and for each phase of a multi-phase VR.
Moreover, in a conventional hybrid PWM controller, no clock domain is associated with either the leading or trailing edge of the phase-shifted pulse. Such a conventional hybrid PWM controller is thus asynchronous.
Specifically, the set (S) and reset (R) inputs to the SR flip-flop are generated by combinational logic and delayed through the DLL. Moreover, the S and R inputs may be delayed by different amounts, and thus may be asynchronous with respect to one another. These factors may lead to glitches on the inputs of the SR flip-flop, which may result in improper execution of the pulse. This may be exasperated at higher switching frequencies as DLL resolution becomes comparable to delays through the combinational logic and setup and hold times of the SR flip flop, which may lead to non-uniform and/or non-monotonic duty cycles, which may result in voltage fluctuations on the regulated voltage rail.
Manual modifications may be made to a conventional hybrid PWM controller and/or an associated VR to improve linear and monotonic operation across PVT variations. This may, however, involve relatively extensive verification and validation processes. Such a system may not be considered a readily-synthesizable design and may negate benefits of digital control.
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